Optical disks are becoming increasingly prevalent for the use of recording information. One form of optical recording disks is CD-R or recordable compact disk. The Photo CD is an example of CD-R disk. Typically, this type of disk has a transparent substrate, a recording layer formed on a substrate, and a reflective layer on the recording layer. The recording layer is essentially a photo absorption material made of mixture of some organic dye materials and is deposited by spin coating. The recording materials used for CD-R applications have been described in U.S. Pat. Nos. 4,940,618; 5,604,004; 5,294,471; European Patent Application 0353393; and Canadian Patent 2,005,520. Commercially useful materials of the type described in these references have stringent requirements. One of the requirements is the light stability. Since Photo CD is a consumer product, it must be capable of withstanding extreme environment. The stability of the disk depends on the nature of the recording layer, the reflector layer, and their mutual interaction. The prior arts cited above disclose phthalocyanine dye, metallized formazan dye and cyanine dye that possesses excellent light stability. The reflecting layer is usually selected to be gold or gold alloy because of their inertness and high reflectivity. The CD-R specifications require that it has a high reflectivity of more than 60% similar to the compact disks.
During recording, writing laser light passes through the transparent polycarbonate substrate and is focused on the dye recording layer which is heated to change the dye material to form a mark. In other recording materials, recording pits are formed. The reflectivity of a mark is lower than those areas not having the mark. The light passes through the unrecorded area and is reflected back by the reflective layer. The record thus consists of marks of relatively low reflectivity on a background of relatively high reflectivity in relation to the read beam and further enhances the process of forming the mark.
Thin layer of gold is normally used as a reflecting layer. Gold is a noble metal with a very high stability and does not affect the recording stability. Materials other than gold such as aluminum, silver and copper and their alloys have high reflectivity but are not useable because they are reactive and can form oxides or other corrosion products. The data recorded in these types of disks degrades over time. However, materials such as silver are much less expensive than gold, and it would be highly desirable to use them.